Fancy dress beginning with a lot of paper (5)
I believe the answer is:
dream
'fancy' is the definition.
(both can mean a fantasy)
'dress beginning with a lot of paper' is the wordplay.
'beginning' says to take the initial letters.
'with' is a charade indicator (letters next to each other).
'a lot of paper' becomes 'ream' (I've seen this in another clue).
The first letter of 'dress' is 'd'.
'd'+'ream'='DREAM'
(Other definitions for dream that I've seen before include "Sleeping thoughts" , "It's experienced during sleep" , "Illusion" , "Reverie or nightmare" , "Fantasy; ideal" .)